In a radio communication system, an extension connection service using a mobile station (MS) is known. This radio communication system includes a plurality of mobile multi-media switching centers (MMSs) which are connected in such a way as to be communicated with each other.
A radio network controller (RNC) is connected to each MMS, to which a plurality of base transceiver stations (BTSs) and extension server devices (extension servers) are connected. The extension server has a function to loop back data and enables intra-office communications. Each MS communicates with a BTS by radio.
In such a radio communication system, communications are conducted between MSs by setting a communication line between RNCs through an MMS and an extension connection service is provided using an outdoor line (a public line, an internet protocol (IP) router network). Thus, for example, an extension connection can be possible between a location A in Kawasaki and a location B in Hiroshima.
A communication system for selecting an optimal communication path from among a plurality of communication paths including a public network and a dedicated line is also known (for example, see Patent documents 1 and 2).    Patent document 1: Japanese National Publication of International Patent Application No. 2001-503578    Patent document 2: Japanese Laid-open Patent Publication No. 2008-061047